The present invention relates to a holographic screen for use in, for example, a rear projection screen. More particularly, the present invention is directed to a holographic screen including convex protrusions having light diffusion and/or light scattering functions.
A conventional rear projection screen contains a diffusion material, and commonly use a lenticular lens and a Fresnel lens. However, such a lenticular-Fresnel screen has a narrow angle of view and limited luminescence. A holographic screen has been proposed, as a result of research that has been conducted in the development of a screen that overcomes these problems.
Since holographic screens are manufactured easily once a master is fabricated and the features of the screen can be adjusted freely, holographic screens have become popular for use in rear projection screens.
FIG. 1 is a perspective view showing part of a conventional holographic screen including convex protrusions having light diffusion and/or light scattering functions.
The holographic screen can be made in a variety of shapes, and primarily includes a Fresnel lens sheet 2 and a holographic sheet 4. The holographic screen is made of a polymer of a transparent acryl-group such as acryl and polymethylmetacrylate (PMMA). Projection light incident from a light source (not shown) is incident to the surface of the Fresnel lens sheet 2. The Fresnel lens sheet 2 has an uneven shape on the surface opposite the light source, which varies a focal point of projection light incident from the light source. Thus, the projection light transmitting the Fresnel lens sheet 2 has a substantially uniform light characteristic on the surface of the screen.
The projection light passed through the Fresnel lens sheet 2 is incident to the holographic sheet 4. The holographic sheet 4 is formed on the viewing surface of the holographic screen, and includes a plurality of diffusion protrusions 6 and a plurality of scattering protrusions 8 which protrude from the viewing surface of the screen. The diffusion protrusions 6 are disposed in predetermined intervals along the horizontal and vertical directions on the surface of the holographic sheet 4. The scattering protrusions 8 are formed over the entire viewing surface of the holographic sheet 4 that includes the diffusion protrusions 6. Respective scattering protrusions 8 have a minute size compared with each of the diffusion protrusions 6. The light incident from the Fresnel lens sheet 2 to the holographic sheet 4 is diffused by the diffusion protrusions 6 and is scattered by the scattering protrusions 8. Most of the light incident to the holographic sheet 4 projects onto the viewing surface via the diffusion protrusions 6. The diffusion protrusions 6 and the scattering protrusions 8 formed on the diffusion protrusions 6 form an image to be viewed by the light passing through themselves. Thus, an area which has no diffusion protrusions 6 becomes dead space with regard to an actual image to be viewed.
When light is incident to the viewing surface of the holographic screen from the surrounding area, the received ambient light causes irregular reflection on the viewing surface of the holographic screen, thereby lowering the contrast of an image.